1. Field of the Invention
The present invention relates to the field of integrated circuits; more specifically, it relates to the communication circuits in integrated circuit chips containing voltage islands.
2. Background of the Invention
A voltage island is a group of circuits powered from the same voltage supply (different from the normal or global chip power supply), the power bus structure needed to distribute the voltage island power supply to the group of circuits, any functions needed to generate or switch between the voltage island power supply and the normal chip power supply, and any control elements needed to perform clock and power management, state saving, power sensing and input or output fencing during voltage changes.
A single chip design may implement several voltage islands, which simultaneously operate at the same or different voltages, yet must still be able to reliably communicate with one another and the rest of the chip. For example, the global voltage supply may be about 1 volt in order to reduce power consumption by the chip, but a voltage island containing special logic circuits may be supplied with a voltage island power supply of 3 volts in order to increase the performance of the logic circuit. Such a chip design may have global circuits, which are always powered on whenever at least one of the voltage islands is powered on, or may have global circuits that are not powered on whenever at least one of the voltage islands is powered on. The global power supply voltage value and individual voltage island power voltage values may vary substantially.
Further, as voltages change state, go from on to off or from off to on, it is necessary that communications between circuits in voltage islands and/or between voltage island circuits and global circuits be prevented from propagating unknown or indeterminate states or voltage values.
Therefore, there is a need for a distinct class of circuits to facilitate the communication between voltage islands or between voltage islands and global chip circuits that are well behaved over a wide range of voltage values even when some of the islands are selectively powered off.
Summary of the Invention
A first aspect of the present invention is an integrated circuit comprising: a first circuit adapted to be powered by a first power supply, the first circuit adapted to send a first signal referenced to the voltage of the first power supply to a second circuit adapted to be powered by a second power supply, the second circuit adapted to receive the first signal and adapted to convert the first signal to a second signal of the same logical value as the first signal and referenced to the voltage of the second power supply.
A second aspect of the present invention is an integrated circuit comprising: a first circuit adapted to be powered by a first and a second power supply, the first circuit adapted to send a first signal referenced to the voltage of the second power supply to a second circuit adapted to be powered by the second power supply and a third power supply, the second circuit adapted to receive the first signal and converting the first signal to a second signal of the same logical value as the first signal and referenced to the voltage of the third power supply.